// dom.style.color = 'red'
// dom.style.fontSize = '12px'
let btn = document.getElementsByClassName('btn')[0]
btn.onclick = function () {
  let title = document.querySelector('.title')
  title.style.color = '#ffffff'
  title.style.fontSize = '20px'
  title.style.lineHeight = '30px'
  title.style.backgroundColor = '#409eff'
}
